Armor wire strength members used in wireline cables for oilfield applications are often composed of galvanized improved plow steel (GIPS). In GIPS armor wire strength members, the steel substrate is coated with zinc via a hot dip galvanization process. The hot dip galvanization process involves immersion of the steel substrate in molten zinc at a temperature of around 860° F. (460° C.).
The strength and hardness of unalloyed zinc are greater than those of tin or lead, but less than those of aluminum or copper. Except when very pure, zinc is brittle at ambient temperatures, but zinc becomes ductile at around 100° C. Pure zinc rapidly recrystallizes after deformation at ambient temperature because of the high mobility of the atoms within the lattice. Thus, zinc typically cannot be work-hardened at ambient temperature.
Hot dip zinc coatings provide corrosion protection in a range of atmospheric and low temperature aqueous environments such as humid atmospheric conditions, natural weathering conditions, soil environments, salt-spray testing conditions and under low temperature aqueous/brine immersion conditions. This corrosion protection may be relevant when GIPS armor wire components of wireline cables are stored between wireline logging operations.
Zinc-based coatings may fall into several categories: pure zinc, zinc-iron, zinc-aluminum, zinc-nickel and zinc composites. In terms of manufacturing methods, zinc coatings are produced by hot-dipping, electroplating, mechanical bonding, sherardizing and thermal spraying. The hot-dip methods are further divided into two processes: (1) the continuous process in which long strands of sheet, wire or tubing are continuously fed through a bath of molten zinc; and (2) the batch process in which fabricated parts such as fasteners, poles or beams are dipped into molten zinc, either individually or in discrete batches. Similarly, zinc electroplating can be performed in a continuous or batch mode.